JP2001217652A - Crystal oscillation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystal oscillation circuit which can suppress an excitation level, while holding the gain of an inverting amplifier circuit and reduce the magnitude of a current flowing into the crystal vibrator. SOLUTION: The crystal oscillation circuit is constituted, by connecting inverting amplifier circuits (2, 10) and phase shift circuits (3, 4, 5, 6), including a crystal vibrator 3 between the input/output terminals of the inverting amplifier circuits, which have limiter circuits (D1, D2) at their output parts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal oscillating circuit, and more particularly to a crystal oscillating circuit suitable for externally connecting another circuit element including a crystal oscillator to an LSI using an inverter on the LSI. About.

[0002]

2. Description of the Related Art FIG. 4 shows a basic configuration of a conventional crystal oscillation circuit using a CMOS inverter. In FIG. 1, the crystal oscillation circuit includes an inverting amplifier circuit including a CMOS inverter 1 and a feedback resistor 2 connected between the input and output terminals of the CMOS inverter 1, and is connected between the input and output terminals of the inverting amplifier circuit. And a phase shift circuit including a crystal oscillator 3, a resistor 4, and capacitors 5 and 6. CMOS inverter 1
Comprises a PMOS transistor Q1 and an NMOS transistor Q2. The source of the PMOS transistor Q1 is supplied with a power supply voltage VDD (for example, 5 V).
The source of the transistor Q2 has a power supply voltage Vss (for example,
0V) is supplied. PMOS transistor Q1 and NM
The gate of the OS transistor Q2 is connected to the input terminal 100, and the drains of the PMOS transistor Q1 and the NMOS transistor Q2 are connected to the output terminal 101.

The CMOS inverter 1 is formed in an LSI, and has a feedback resistor 2 and a phase shifter composed of a crystal oscillator 3, a resistor 4, and capacitors 5, 6 connected between input and output terminals of an inverting amplifier circuit. The circuit has input terminal 100, output terminal 1
01 externally.

[0004]

In the above configuration, the output amplitude of the inverting amplifier makes a full swing between the power supply voltage VDD and the power supply voltage Vss during the oscillation operation. As a result, the amount of current flowing into the node N1, that is, the amount of current flowing into the crystal resonator 3 increases. FIG. 5 shows an equivalent circuit of the crystal unit 3. As shown in the figure, the crystal resonator 3 is represented as a circuit in which a series circuit of an inductance L1, a capacitor C1, and a resistor CI and a capacitor C0 are connected in parallel.

At this time, assuming that the maximum value of the instantaneous value Id of the current flowing into the crystal oscillator 3 is Idmax, the excitation level X of the conventional crystal oscillation circuit shown in FIG. 4 is X = (Idmax / √2) ²
× CI. Therefore, if the current value Idmax is large,
The excitation level X of the crystal oscillation circuit becomes large, and in some cases, there is a problem that the crystal resonator may be thermally destroyed. The present invention has been made in view of such circumstances, and it is possible to suppress the excitation level while maintaining the gain of the inverting amplifier circuit, and to reduce the amount of current flowing into the crystal resonator. It is intended to provide a circuit.

[0006]

In order to achieve the above object, according to the first aspect of the present invention, there is provided an inverting amplifier circuit and a phase shift circuit including a crystal oscillator between input and output terminals of the inverting amplifier circuit. In the connected crystal oscillation circuit, the inverting amplifier circuit has a limiter circuit in an output unit.

According to a second aspect of the present invention, there is provided a crystal oscillation circuit comprising an inverting amplifier circuit and a phase shift circuit including a crystal oscillator connected between input and output terminals of the inverting amplifier circuit. The circuit includes a CMOS inverter, and connects the drain of the PMOS transistor and the drain of the NMOS transistor forming the CMOS inverter via a serial circuit in which two rectifying elements are connected in series in the forward direction. Wherein the connection point of the two rectifying elements is an output terminal of the inverting amplifier circuit.

[0008] Further, the invention described in claim 3 is based on claim 2.
Wherein the rectifying element is a diode-connected MOS transistor.

According to the crystal oscillation circuit of the present invention, there is provided a crystal oscillation circuit in which an inverting amplifier circuit and a phase shift circuit including a crystal oscillator are connected between input and output terminals of the inverting amplifier circuit. Since the limiter circuit is provided at the output section of the inverting amplifier circuit, the excitation level can be suppressed while maintaining the gain of the inverting amplifier circuit, and the amount of current flowing into the crystal resonator can be reduced. .

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a configuration of a crystal oscillation circuit according to an embodiment of the present invention. In FIG. 1, components having the same functions as the components of the conventional crystal circuit shown in FIG. 4 are denoted by the same reference numerals. The crystal oscillation circuit according to the embodiment of the present invention is different from the conventional crystal circuit shown in FIG. 4 in configuration in terms of an inverting amplifier circuit and a transfer circuit including a crystal oscillator between input and output terminals of the inverting amplifier circuit. In the crystal oscillation circuit having the phase circuits connected, a limiter circuit is provided at the output section of the inverting amplifier circuit, and other configurations are the same.

In FIG. 1, the crystal oscillation circuit is a CMOS
An inverting amplifier circuit comprising an inverter 10 and a feedback resistor 2 connected between the input and output terminals of the CMOS inverter 10;
It has a crystal oscillator 3, a resistor 4, and capacitors 5 and 6 connected between the input and output terminals of the inverting amplifier circuit. The CMOS inverter 10 includes a PMOS transistor Q1, an NMOS transistor Q2, a PMO
A series circuit in which diodes D1 and D2 as two rectifiers are connected in series in the forward direction and connected between the drain of the S transistor Q1 and the drain of the NMOS transistor Q2, and the source of the PMOS transistor Q1 is a power supply voltage. VDD (for example, 5 V) is supplied, and the source of the NMOS transistor Q2 is supplied with the power supply voltage Vss (for example, 0 V).
V).

The gates of the PMOS transistor Q1 and the NMOS transistor Q2 are connected to an input terminal 100, and the drains of the PMOS transistor Q1 and the NMOS transistor Q2 are connected to an output terminal 101. The CMOS inverter 10 is formed in an LSI, and a phase shift circuit composed of a feedback resistor 2 and a crystal oscillator 3, a resistor 4, and capacitors 5 and 6 connected between input and output terminals of an inverting amplifier circuit has an input. It is externally connected via a terminal 100 and an output terminal 101. The series circuit of the diodes D1 and D2 functions as a limiter that limits the amplitude of the output voltage of the CMOS inverter 10 according to the offset voltage characteristics of the diodes. FIG. 2 shows the voltage (V) -current (I) characteristics of the diode.
Shown in In the figure, VF is an offset voltage.

In the above configuration, when a noise component such as thermal noise is input from the input terminal 100 when the power is turned on, the CMO
The signal is amplified by an inverting amplifier circuit composed of the S inverter 10 and the feedback resistor 2, but the amplitude is limited by a limiter composed of a series circuit of diodes D1 and D2. That is, as shown in FIG. 3, in the section where the PMOS transistor Q1 is turned on, a current flows to the output terminal 101 via the diode D1 according to the change of the AC voltage input to the input terminal 100, and the output at the output terminal 101 The voltage is amplitude-limited to the negative side from the power supply voltage VDD by the offset voltage VF. In a section where the NMOS transistor Q2 is turned on, the power supply Vss is output from the output terminal 101 via the diode D2 and the NMOS transistor Q2.
Therefore, the output voltage at the output terminal 101 is amplitude-limited to the plus side from the power supply voltage Vss by the offset voltage VF.

As described above, according to the crystal oscillation circuit according to the present embodiment, in the conventional inverting amplifier, the output terminal 101
Output swing at the full swing between the power supply voltage VDD and the power supply voltage Vss, whereas in the crystal oscillation circuit according to the present embodiment, the output amplitude at the output terminal 101 is the offset voltage of the diodes D1 and D2. Since the voltage waveform is clipped by VF, the excitation level can be suppressed while maintaining the gain of the inverting amplifier circuit, and the amount of current flowing into the crystal resonator can be reduced. The diodes D1 and D2 may be formed by connecting MOS transistors in a diode manner.

Further, in the present embodiment, the inverting amplifier circuit is constituted by only one CMOS inverter. However, the present invention is not limited to this configuration. A limiter may be provided. Further, in the present embodiment, the inverting amplifier circuit is
Although the configuration is made using the OS inverter, a similar effect can be obtained by using a bipolar transistor.

[0016]

As described above, according to the crystal oscillation circuit according to any one of claims 1 to 3, a phase shift circuit including an inverting amplifier circuit and a crystal oscillator between input and output terminals of the inverting amplifier circuit. Since the limiter circuit is provided at the output section of the inverting amplifier circuit in the crystal oscillator circuit connected to the above, the excitation level can be suppressed while maintaining the gain of the inverting amplifier circuit, and the current flowing into the crystal oscillator can be suppressed. The amount of current generated can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a crystal oscillation circuit according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing voltage-current characteristics of a diode used as a limiter in the crystal oscillation circuit shown in FIG.

FIG. 3 is a diagram showing an output voltage waveform of an inverting amplifier in the crystal oscillation circuit shown in FIG.

FIG. 4 is a circuit diagram showing a configuration of a conventional crystal oscillation circuit.

FIG. 5 is a circuit diagram showing an equivalent circuit of a crystal resonator in the crystal oscillation circuit shown in FIG.

[Explanation of symbols]

 1, 10 CMOS inverter 2 feedback resistor 3 crystal oscillator 5, 6 capacitor D1, D2 diode Q1 PMOS transistor Q2 NMOS transistor 100 input terminal 101 output terminal

Claims (3)

[Claims] 1. A crystal oscillation circuit comprising an inverting amplifier circuit and a phase shift circuit including a crystal oscillator connected between input and output terminals of the inverting amplifier circuit, wherein the inverting amplifier circuit has a limiter circuit in an output section. A crystal oscillation circuit comprising: 2. A crystal oscillation circuit comprising an inverting amplifier circuit and a phase shift circuit including a crystal oscillator connected between input and output terminals of the inverting amplifier circuit, wherein the inverting amplifier circuit includes a CMOS inverter. A drain of a PMOS transistor and a drain of an NMOS transistor constituting the CMOS inverter are connected via a series circuit in which two rectifying elements are connected in series in a forward direction, and a connection point of the two rectifying elements in the series circuit. Is the output terminal of the inverting amplifier circuit. 3. The crystal oscillation circuit according to claim 2, wherein the rectifier is a diode-connected MOS transistor.